1. Field of the Invention
The present invention relates to a predictive coding apparatus, control method thereof, and a computer program.
2. Description of the Related Art
An example of a moving picture coding schemes is MPEG-4 AVC: ISO/IEC 14496-10, also known as H.264 (to be referred to as MPEG-4 AVC), which is employed in digital television broadcasting and video recording media. MPEG-4 AVC adopts the following two context-based entropy coding schemes to increase coding efficiency, compared to conventional entropy coding schemes:                Context-based Adaptive Variable Length Coding (CAVLC)        Context-based Adaptive Binary Arithmetic Coding (CABAC)        
Of these schemes, CABAC performs arithmetic coding as follows. Binarization processing is done for data to be coded to calculate the probability of occurrence of binary data (bin) in accordance with the context (current coding target and surrounding circumstances). The calculation result is then set as coded data. The length of binary data output by binarization processing varies depending on a video signal input to a coding apparatus as well as coding conditions. As such, it is recognized that an enormous amount of binary data may be generated due to its property. CABAC has problems such as a fear about assurance of real-time arithmetic coding processing for binary data, and inability of deciding in advance a memory area to store generated binary data.
To solve these problems, there is a proposed method for suppressing the binary data amount in coding. Japanese Patent Laid-Open No. 2007-020141 proposes a method for subtracting an offset value from an orthogonally transformed value and then quantizing the value in order to reduce the amount of binary data generated by binarization processing so that it becomes smaller than that of binary data generated by original binarization processing. Japanese Patent Laid-Open No. 2007-020141 proposes even a method for selecting a motion vector which reduces the binary data amount, compared to coding with a motion vector which provides the smallest evaluation value in motion vector detection.